Boss CE-2 Distorts

[sfx1999]

I built the Tonepad Boss CE-2 clone. I used 2n5089's instead of 2n5088's and a TL072 instead of the 4558. I did not mod it. I used metal film resistors and ceramic disc capacitors. It was working great, but now it distorts the signal; it is a fuzz type sound. Does anyone have advice as to where to look for the source of this distortion? The distortion does NOT depend on the position of the knobs. Another thing I was wondering, could this be some sort of oscillation I am mistaking for fuzz? I was thinking that using such a high impedance op amp could have caused a problem, but if that were the case, it should have done that before. My other thought was that some sort of mechanical shock screwed up part of the circuit.

[Andre]

It looks like the BBD's bias setting is wrong.
What happens if you turn the trimpot?

You can easily set this trimpot without an oscilloscope.
First rotate it to one side until distortion starts, then turn to the other side until distortion starts.
Now set the trimpot in the middle of these two points and you're done.

André

[sfx1999]

That was the problem. I didn't realize that the trimpot sets the bias for the BBD; I thought it was only to set the ground. It didn't really say that in the project PDF.